1. Field of the Invention
The present invention relates to a process for the preparation of methacrylic acid esters by esterification of methacrylic acid with a lower aliphatic alcohol.
2. Description of the Prior Art
In preparing methacrylic acid esters in the liquid phase, using an acidic solid catalyst, the reaction product contains large amounts of unreacted methacrylic acid because the esterification reaction is an equilibrium reaction. Therefore it is necessary to separate unreacted methacrylic acid from the esterification product in order to reuse it as the raw material of the esterfication reaction.
According to the prior art, after separating unreacted methacrylic acid from the esterification product by distillation or flash vaporization (methacrylic acid separation step), unreacted alcohol is separated, and then the methacrylic acid ester is rectified. (Japanese Patent Publication No. 1369/73). The above method, however, has certain disadvantages because the formed ester, water and unreacted alcohol must be all vaporized in the methacrylic acid separation step in order to separate unreacted methacrylic acid.
Hence a need has continued to exist for an improved process for separating methacrylic acid from the esterfication reaction mixture.